ABSTRACT
Over the last few decades, key problems of petrology of mafic-ultramafic complexes (massifs) of different types in different crustal structures have been discussed, with emphasis on massifs belonging to ophiolite associations. The aspects concerned were their structural position; bedding conditions; internal structure; spatial and age relations between ultramafic and gabbroid bodies; rock, mineral, major-and traceelement, and isotope compositions; time and possible conditions of generation of melts and their emplacement into the crust; and composition of deep-seated sources of material. It has been established that mafic-ultramafic massifs can be considerably different in structural position, bedding conditions and age, size, morphology, internal structure, relationship between the volumes of ultramafic rocks and gabbroids at the presentday erosion level, petrographic composition, petrochemical and isotope-geochemical characteristics, and metallogeny. It has been found that ophiolite associations and constituent mafic-ultramafic massifs have a belt-like structure and mark zones of long-lived deep-seated faults and feathering faults; at the present-day erosion level, most of these massifs are elongated lens-shaped objects with steeply inclined contacts. On the other hand, massifs at the intersection of faults which experienced fold-block deformations are often of irregular or subisometric shape and show gentle bedding. The length of massifs is from few hundreds of meters to tens and hundreds of kilometers, and their width is from few tens of meters to few tens of kilometers. Massifs can outcrop in areas of fractions of a square kilometer to several thousands of square kilometers. By relationships between the areas of ultramafic-and mafic-rock outcrops, massifs vary from almost “monogene’’ ultramafic bodies and complex mafic-ultramafic bodies to almost “monogene’’ gabbroid bodies.
